Victron MPPT keeps dropping to float way too early — anyone else had this?

Had this exact issue last summer with my 100/20 on the garden office setup. Drove me absolutely mental for weeks.

Turned out my battery voltage sensing was off — the MPPT was reading at the controller terminals rather than at the battery itself, so voltage drop across the cable was making it think the battery was fuller than it was. Switched to remote voltage sensing via the VE.Direct cable and a BMV-712 and it sorted it almost immediately.

A few things worth checking:

• Cable sizing — undersized cable between controller and battery causes voltage drop that fools the MPPT
• Absorption voltage setting — what have you got it set to? If it's too low, it'll hit float much sooner than expected
• Battery type profile — if you're on a Fogstar or similar lithium, make sure you're not accidentally running a lead-acid profile
• Temperature — Victron's temperature compensation can knock the absorption voltage down on warmer days, which shortens the absorption phase

Also worth checking whether it's actually a problem at all. If your battery is genuinely getting to 80-90% SOC fairly quickly (smaller battery bank, modest loads), hitting float "early" can be totally normal behaviour and not a fault.

What's your setup — panel wattage, battery capacity, cable runs? That'd help narrow it down. I've seen people panic about this and it's just their system working correctly, but I've also seen genuine configuration issues that waste a significant chunk of available solar.

Anyone else had the remote sensing fix work for them? Curious whether that's a common one or I just got unlucky with my initial install.

My Victron 100/30 did the same thing charging the shepherds hut batteries — turns out the cable run to the Fogstar Drift LiFePO4 was long enough that the voltage drop was basically lying to the controller like a dodgy used car salesman.

Yeah had this on my van conversion last year. Worth checking your absorption time settings in VictronConnect — if it's set too short it'll bail out early regardless of actual battery state.

Also had a dodgy temp sensor throwing the voltage compensation way off, which made the controller think the batts were fuller than they were. Pulled the sensor and it sorted itself.

@FogstarGal cable voltage drop is a big one too — even 0.2V difference can confuse it badly.

Decent write-up of the common causes here on the Victron community forums if you've not already had a rummage around there.

Bonus pro tip: if your Victron is making decisions based on dodgy voltage readings, just remember it's essentially a very expensive thermostat that gave up early — same as me on a cold Monday morning.

@WonkyMender absorbed that advice faster than my 100/20 absorbs literally nothing before screaming "float time!" at 11am on a cloudy day 😂

Seriously though — had this exact drama on the narrowboat last winter, and the culprit nobody's mentioned yet is temperature compensation. If your Victron is using the default 25°C charge curve but your battery bank is sitting in a cold bilge at 8°C, it'll hit the voltage threshold early and bail to float like it's done a full day's work.

Stick a Smart Battery Sense in the loop — mine transformed the whole system overnight. The MPPT actually talks to it properly via Bluetooth and adjusts accordingly. Worth every penny of the ~£35 it costs.

Great thread to stumble across — and welcome to the forum @HannahDavies85, love seeing new members jumping straight into the technical banter 😄

One thing nobody's mentioned yet: adaptive absorption. If your Victron is using it, the first charge cycle after a reset sets the benchmark — if that initial cycle was abnormally short (say, batteries weren't actually depleted), every subsequent absorption phase gets calculated shorter than it should be.

Worth resetting the adaptive algorithm entirely via VictronConnect and doing a proper full discharge/recharge cycle to recalibrate it.

Also check your tail current setting — if it's set too high (I had mine at 4% accidentally), the controller interprets normal resting current as "battery full" and boots straight to float prematurely.

@HannahDavies85 that 11am float complaint is painfully familiar — spent a whole autumn convinced my Fogstar 100Ah LiFePO4 was dying, turned out the MPPT was measuring at the controller rather than the battery terminals.

Ran a proper voltage drop test across the cable run and found nearly 0.4V of difference. Once I set up remote battery sensing through the VE.Direct cable to a BMV-712, the absorb phase actually started lasting a sensible amount of time again.

Worth checking your cable gauge and run length too. My static van install had undersized cable from a previous owner — classic false economy that causes no end of confusion downstream.